Some modern missile systems utilize on board aiming devices such as a strapdown inertial measurement unit (IMU). Typically, the inertial measurement unit is comprised of three gyros and three accelerometers with electronics (including a computer) to define and maintain a reference coordinate system from which velocity and position can be derived. However, unless an extremely accurate vertical gyro is utilized, accurate self-contained alignment of strapdown inertial measurement units cannot be realized without some form of augmentation such as indexing the inertial measurement unit, or as a minimum, indexing the vertical gyro through either 90 degrees or 180 degrees for determining short term gyro drift, i.e., the gyro is calibrated just prior to using it for azimuth heading determination. An extremely accurate vertical gyro or an augmentation technique, in general, adds cost and complexity to a unit which is ultimately expended.
It is therefore, an object of the present invention to provide apparatus for fast, accurate azimuth aiming of a strapdown inertial measurement unit on board a missile.
It is a further object of the present invention to provide such apparatus as part of a launch vehicle, and therefore, is not expended with the missile but is used repeatedly with each reload.